5 Interactions of Beams with Surroundings
197
• minimize the risk of damage of the detectors by beam loss and irradiation;
• minimize the size of the beam pipe in the detector region to allow for the
installation of vertex detectors as close as possible to the interaction region;
• maximize the space available for the detector and the solid angle coverage down
to low angles close to the beam.
These are rather conflicting requirements. Minimizing the size of the beam pipe
for installation of sensitive vertex detectors close to the beam pipe will increase
the background rates hitting the detector region and increase the risk of damage by
beam loss. The requirements for maximum space and solid angle coverage for the
detectors are also in conflict with the requirements of the accelerator to maximize
luminosity by
• allowing for space close to the interaction point for final focus quadrupoles;
• reducing the β-function at the interaction point, which increases the beam size
in the final focus quadrupoles with the risk to create local aperture limits and
losses and which limits the space and low angle coverage available for particle
detection;
• installation of beam-separators close to the interaction region to allow to fill the
machine with many bunches.
It is essential to consider the accelerator and detector requirements together, both
during the design stage and also later in the optimization of the running parameters.
Experience shows that it typically takes several years to commission and
optimize the performance of a new accelerator. During these first years, it will often
be possible to increase the luminosity without compromising on the experimental
conditions for the detectors. Detailed simulation and continuous monitoring of
the background conditions are important to identify potential limitations, to guide
further optimization and to identify the potential for upgrades towards higher
luminosities or smaller beam pipes.
Different types of backgrounds and their mitigation with examples from LEP and
LHC are now discussed.
5.3.1 Sources of Detector Background and Detector
Performance
It is possible to distinguish between two main types of machine induced backgrounds
• backgrounds induced by losses of beam particles;
• background from synchrotron radiation, relevant for high energy e + , e − beams.
197
• minimize the risk of damage of the detectors by beam loss and irradiation;
• minimize the size of the beam pipe in the detector region to allow for the
installation of vertex detectors as close as possible to the interaction region;
• maximize the space available for the detector and the solid angle coverage down
to low angles close to the beam.
These are rather conflicting requirements. Minimizing the size of the beam pipe
for installation of sensitive vertex detectors close to the beam pipe will increase
the background rates hitting the detector region and increase the risk of damage by
beam loss. The requirements for maximum space and solid angle coverage for the
detectors are also in conflict with the requirements of the accelerator to maximize
luminosity by
• allowing for space close to the interaction point for final focus quadrupoles;
• reducing the β-function at the interaction point, which increases the beam size
in the final focus quadrupoles with the risk to create local aperture limits and
losses and which limits the space and low angle coverage available for particle
detection;
• installation of beam-separators close to the interaction region to allow to fill the
machine with many bunches.
It is essential to consider the accelerator and detector requirements together, both
during the design stage and also later in the optimization of the running parameters.
Experience shows that it typically takes several years to commission and
optimize the performance of a new accelerator. During these first years, it will often
be possible to increase the luminosity without compromising on the experimental
conditions for the detectors. Detailed simulation and continuous monitoring of
the background conditions are important to identify potential limitations, to guide
further optimization and to identify the potential for upgrades towards higher
luminosities or smaller beam pipes.
Different types of backgrounds and their mitigation with examples from LEP and
LHC are now discussed.
5.3.1 Sources of Detector Background and Detector
Performance
It is possible to distinguish between two main types of machine induced backgrounds
• backgrounds induced by losses of beam particles;
• background from synchrotron radiation, relevant for high energy e + , e − beams.